Smartphone assisted naked eye detection of mercury (II) ion using horseradish peroxidase inhibitive assays

Background: Mercury (II) ion, Hg2+ is among the most common pollutants with the ability to affect the environment. The implications of their elevation in the environment are mainly due to the industrialization and urbanization process. Current methods of Hg2+ detection primarily depend on sophisticated and expensive instruments. Hence, an alternative and practical way of detecting Hg2+ ions is needed to go beyond these limitations. Here, we report a detection method that was developed using an inhibitive enzymatic reaction that can be monitored through a smartphone. Horseradish peroxidase (HRP) converted 4-aminoantipyrene (4-AAP) into a red colored product which visible with naked eye. A colorless product, on the other hand, was produced indicating the presence of Hg2+ that inhibit the reaction. Objectives: The aim of this study is to develop a colorimetric sensor to detect Hg2+ in water sources using HRP inhibitive assay. The system can be incorporated with a mobile app to make it practical for a prompt in-situ analysis. Methods: HRP enzyme was pre-incubated with different concentration of Hg2+ at 37°C for 1 hour prior to the addition of chromogen. The mix of PBS buffer, 4-AAP and phenol which act as a chromogen was then added to the HRP enzyme and was incubated for 20 minutes. Alcohol was added to stop the enzymatic reaction, and the change of colour were observed and analyse using UV-Vis spectrophotometer at 520 nm wavelength. The results were then analysed using GraphPad PRISM 4 for a non-linear regression analysis, and using Mathematica (Wolfram) 10.0 software for a hierarchical cluster analysis. The samples from spectroscopy measurement were directly used for dynamic light scattering (DLS) evaluation to evaluate the changes in HRP size due to Hg2+ malfunctionation. Finally, molecular dynamic simulations comparing normal and malfunctioned HRP were carried out to investigate structural changes of the HRP using YASARA software. Results: Naked eye detection and data from UV-Vis spectroscopy showed good selectivity of Hg2+ over other metal ions as a distinctive color of Hg2+ is observed at 0.5 ppm with the IC50 of 0.290 ppm. The mechanism of Hg2+ inhibition towards HRP was further validated using a dynamic light scattering (DLS) and molecular dynamics (MD) simulation to ensure that there is a conformational change in HRP size due to the presence of Hg2+ ions. The naked eye detection can be quantitatively determined using a smartphone app namely ColorAssist, suggesting that the detection signal does not require expensive instruments to be quantified. Conclusion: A naked-eye colorimetric sensor for mercury ions detection was developed. The colour change due to the presence of Hg2+ can be easily distinguished using an app via a smartphone. Thus, without resorting to any expensive instruments that are mostly laboratory bound, Hg2+ can be easily detected at IC50 value of 0.29 ppm. This is a promising alternative and practical method to detect Hg2+ in the environment

Whole-genome sequencing and annotation of Bacillus safensis RIT372 and Pseudomonas oryzihabitans RIT370 from Capsicum annuum (bird\u27s eye chili) and Capsicum chinense (yellow lantern chili), respectively

Here, we report the genome sequences of Bacillus safensis RIT372 and Pseudomonas oryzihabitans RIT370 from Capsicum spp. Annotation revealed gene clusters for the synthesis of bacilysin, lichensin, and bacillibactin and sporulation killing factor (skfA) in Bacillus safensis RIT372 and turnerbactin and carotenoid in Pseudomonas oryzihabitans RIT370

A colorimetric assay to detect mercury (II) ions in water sources using conjugated gold-nanoparticles

Rapid industrial progress has led to the elevation of heavy metal concentration in the environment, which raised tacit concerns. Among these metals, mercury (II) ion, Hg2+ is one of the most detrimental to the human health due to its neurotoxic and nephrotoxic properties. To date, methods to determine the presence of Hg2+ ions require expensive equipment and sophisticated operation. This is impractical for a constant monitoring of Hg2+ in water sources. Thus, it is necessary to develop a simple yet effective bio sensing method to monitor Hg2+ level in our environment. Recently, gold-nanoparticles (AuNPs) have attracted considerable amount of attention due to their nature of strong plasmonic resonance which can be exploited for a simple and rapid colorimetric assay. As the distance between nanoparticles decreases, the plasmon energy band is lowered and consequently it turns the colour of AuNPs from red to blue. The key of utilizing this phenomenon as a bio sensing mechanism is to control the AuNPs aggregation via surface chemistry approach. Here, a sensitive and practical colorimetric assay for in-situ detection of Hg2+ ions in water using cysteine functionalized gold nanoparticles (Cys- AuNPs) together with the addition of polyamidoamine (PAMAM), G2 dendrimer is reported. In this study, Cys-AuNPs and PAMAM dendrimer specifically capture Hg2+ ions and induce colour changes of the solution. The mechanism of Hg2+ interaction with the system was investigated using UV-vis spectrophotometer, dynamic light scattering (DLS) and transmission electron microscope (TEM). To increase the practicality value of the system, a custom-made chamber to be integrated with a mobile phone was fabricated. Colour changes can be monitored using a mobile app. The newly developed detection system can detect Hg2+ as low as 0.5 part per billion (ppb) in a laboratory prepared sample or in a real river water sample. The results were validated using direct thermal decomposition mercury analyser. This cost-effective colorimetric approach is practical to determine the presence of Hg2+ water sources